The present invention relates to a charging control of a rechargeable battery.
In recent years, a charger provided with a microcomputer for the purpose of achieving high functionality and efficiency is widely used as a charger for charging various rechargeable batteries such as a nickel hydride rechargeable battery and a lithium ion rechargeable battery. In the charger, the microcomputer controls battery charging based on various information inside the charger and also from a battery pack including a rechargeable battery.
Not only the charger but also the battery pack including a rechargeable battery is now being widely used which is provided with a microcomputer and the microcomputer monitors the state (for example, voltage, temperature and so on) of the rechargeable battery and performs various controls based on various information (for example, voltage, temperature and so on) of the rechargeable battery. As noted above, an enhancement of functionality is facilitated by providing a microcomputer in a charging system which charges a rechargeable battery by connecting a battery pack including the rechargeable battery to a charger.
In a case where a microcomputer controls generation of a charging direct-current power inside the charger or charging to a rechargeable battery inside the battery pack, a software error caused in the microcomputer (software anomaly) or hardware anomaly in the microcomputer inhibits normal control by the microcomputer. The rechargeable battery may not be properly charged.
For example, there is a known charger provided with a microcomputer in which, when the microcomputer outputs a charging permission signal, a converter operates to convert an external input power to a charging direct-current power, while, when a charging stop signal is outputted from the microcomputer, the converter is inhibited from operating. If the charging permission signal continues to be outputted from the microcomputer due to anomaly in the microcomputer of the charger constituted as such, the rechargeable battery continues to be charged regardless of its charged state. The rechargeable battery may not be charged appropriately.
To solve the above problem, one technique is disclosed, for example, in Unexamined Japanese Patent Publication No. 2003-299260 in which the power outputted from the converter is periodically turned off (for 10 ms per second, for example) so as to superimpose a periodic pulse from the microcomputer on the output voltage from the converter, and a watchdog circuit detects the pulse superimposed on the output voltage from the converter. If the pulse is not detected normally, the converter is stopped.